As a brake apparatus for a vehicle or an electronically-controlled brake apparatus for electrically controlling a braking force of the brake apparatus in accordance with a brake operation force, an operation amount, or the like input from a brake pedal, that is, the hydraulic pressure supplied to a wheel cylinder for driving the brake apparatus, an ECB (Electronically controlled Brake) for controlling a braking force by a hydraulic pressure accumulated in an accumulator is known.
In the ECB, the hydraulic pressure boosted by a pump is accumulated in the accumulator and adjusted in response to a brake request of the driver, and the resultant pressure is supplied to the wheel cylinder as the brake apparatus. When the driver operates the brake pedal, a master cylinder generates a hydraulic pressure according to the operation amount. A part of the hydraulic oil flows in a stroke simulator, and the operation amount of the brake pedal is adjusted in accordance with the pedal effort (operation force) on the brake pedal. On the other hand, a brake ECU sets a target reduction speed of the vehicle in accordance with a pedal stroke, determines distribution of braking forces to be applied to the wheels, and a predetermined hydraulic pressure is applied from the accumulator to each of the wheel cylinders.
The ECB sets a proper brake hydraulic pressure according to the brake operation input from the brake pedal and supplies a proper hydraulic pressure from the accumulator to each of the wheel cylinders, thereby electrically controlling the braking force. Consequently, when a power supply unit fails, a proper hydraulic pressure cannot be supplied to the wheel cylinders. There is, for example, a power supply unit for a vehicle disclosed in Patent Document 1 as a technique for making an electronically controlled unit such as a brake apparatus operate normally even when the power supply unit fails.
The power supply unit for a vehicle described in Patent Document 1 includes, as an auxiliary power supply, a power supply backup unit using a capacitor unit made of a plurality of capacitors. The power supply unit has a power supply device that enables power from the capacitor unit to be supplied also when a battery is normal, and a forced-operation device for making the power supply device operate. In a normal state, the operation state of the power supply unit is checked.
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-014754